1. Field of the Invention
This invention relates to a self-expanding mount for supporting a vibration source, such as an engine, on a base such as the chassis of a vehicle, and more particularly to a self-expanding mount of this kind, which has a liquid chamber filled with liquid, the pressure of which is varied in response to vibration transmitted from the vibration source to cause contraction and expansion of a resilient member thereof fixed to the vibration source, to thereby control transmission of the vibration to the base.
2. Prior Art
Conventionally, self-expanding mounts of this kind, which are so-called active mounts, have been proposed e.g. by Japanese Provisional Patent Publication Kokai) No. 60-8540 and U.S. Pat. No. 4,638,983.
The former discloses a vibration-absorbing device comprising a fluid chamber provided between a vibrating body or engine and a vibrated body or chassis of a vehicle, which is filled with fluid and adapted to expand and contract in response to vibration transmitted from the vibrating body, and pulsating pressure-generating means which imparts pulsating pressure to the fluid within the fluid chamber in opposite phase to a pulsation caused by the vibration transmitted from the vibrating body to thereby prevent transmission of vibration from the vibrating body to the vibrated body, wherein the pulsating pressure-generating means is comprised of a vibrating element which is formed of a generally flat plate made of a magnetic material and forming part of walls defining the fluid chamber, the vibrating element being capable of vibrating to thereby impart pulsation to the fluid within the fluid chamber, and a pair of solenoids which, when energized, cause vibration of the vibrating element. In the proposed vibration-absorbing device, the vibrating element in the form of a generally flat plate is vertically vibrated by an electromagnetic force generated by the solenoids to impart vibration to the fluid within the fluid chamber in opposite phase to pulsation caused by vibration of the engine, to thereby prevent the vibration of the engine from being transmitted to the chassis of a vehicle.
The latter discloses an apparatus for the resilient mounting of a vibrating body, including a mounting bracket and a pedestal which are interconnected through a resilient element that contains a liquid-filled hollow space (main liquid chamber), a compensating baffle associated with a positioning element being provided whose adjustment permits compensation of the pressure variations in the liquid caused by disturbing vibrations, wherein the compensating baffle faces the liquid-filled space, the positioning element is adapted to be actuated by a primary element which detects disturbing vibrations of the vibrating body, and the primary element and the positioning element are interconnected through a freely programmable control unit. Further, an equalizing space (auxiliary liquid chamber) is connected to the working space or liquid-filled space through a throttle opening. According to this prior art, when the liquid-filled space is compressed by downward movement of the engine, for example, the compensating baffle is displaced upward to thereby prevent vibration of the engine from being transmitted to the chassis or frame of a vehicle.
According to the former prior art, the solenoids are energized in response to vibration of the engine as a vibrating body, which causes vibration of the vibrating element in the form of a generally flat plate forming part of the fluid chamber to vary the pressure of the fluid within the fluid chamber, which in turn causes expansion and contraction of a resilient member fixed to the engine to thereby prevent vibration of the engine from being transmitted to the chassis of the vehicle. On the other hand, according to the latter prior art, when the primary element supplies an electrical signal to the control unit, the control unit processes the signal on the basis of the engine rotational speed or other parameters and supplies the processed signal to the positioning element to drive same, whereby the compensating baffle is displaced within the liquid-filled space, varying the pressure of the liquid therein, so that the resilient element fixed on the engine side is expanded and contracted to prevent the vibration of the engine from being transmitted to the chassis or frame of the vehicle.
Thus, according to the prior art devices described above, the vibrating element or the compensating baffle as a driven member is displaced within the liquid chamber to vary liquid pressure within the liquid chamber, which causes expansion and contraction of the resilient member defining the liquid chamber and fixed to the engine to thereby prevent the vibration of the engine from being transmitted to the chassis of the vehicle. Therefore, the both prior art devices suffer from a time lag between the time point current is supplied to the solenoids or the control signal is supplied to the positioning element and the time point the resilient member is actually expanded and contracted. The time lag lies within a range of 1 millisec. to several tens millisec., so that engine vibration components in a low frequency region can be absorbed to some extent, but engine vibration components in a high frequency region (e.g. higher than 100 Hz) cannot be absorbed, resulting in transmission of the engine vibration to the chassis of the vehicle.